Autonomic nervous system neurotransmitters

Parasympathetic nervous system. That portion of the autonomic nervous system that utilizes acetylcholine as the neurotransmitter at the neuro-effector junctions. 

Neurotransmitter in the brain and peripheral autonomic nervous system... 

Figure 1. A depiction of the several different ionic currents necessary for the acute function of neuromuscular transmission in the skeletal motor and the efferent autonomic nervous system. The boxed current designations are associated, by the arrows, with those cellular regions where their physiological role is most evident, although these currents often exist in other regions of the cell. = neurotransmitter-activated current ...

Dopamine is a catecholamine neurotransmitter in the CNS and at some ganglia in the autonomic nervous system. To date, three main types of receptors have been found D1( D2, and D3. The main dopaminergic systems in the brain are the nigro-neostriatal... 

For each neurotransmitter in the autonomic nervous system, list the neurons that release it and the type and location of receptors that bind with it... 

Table 9.3 Distinguishing Features of Neurotransmitters of Autonomic Nervous System...

Adrenal medulla. Derived from neural crest tissue, the adrenal medulla forms the inner portion of the adrenal gland. It is the site of production of the catecholamines, epinephrine and norepinephrine, which serve as a circulating counterpart to the sympathetic neurotransmitter, norepinephrine, released directly from sympathetic neurons to the tissues. As such, the adrenal medulla and its hormonal products play an important role in the activity of the sympathetic nervous system. This is fully discussed in Chapter 9, which deals with the autonomic nervous system. 

The autonomic nervous system (ANS) modifies contractile activity of both types of smooth muscle. As discussed in Chapter 9, the ANS innervates the smooth muscle layer in a very diffuse manner, so neurotransmitter is released over a wide area of muscle. Typically, the effects of sympathetic and parasympathetic stimulation in a given tissue oppose each other one system enhances contractile activity while the other inhibits it. The specific effects (excitatory or inhibitory) that the two divisions of the ANS have on a given smooth muscle depend upon its location. 

The concept of chemical neurotransmission originated in the 1920s with the classic experiments of Otto Loewi (which were themselves inspired by a dream), who demonstrated that by transferring the ventricular fluid of a stimulated frog heart onto an unstimulated frog heart he could reproduce the effects of a (parasympathetic) nerve stimulus on the unstimulated heart (Loewi Navratil, 1926). Subsequently, it was found that acetylcholine was the neurotransmitter released from these parasympathetic nerve fibers. As well as playing a critical role in synaptic transmission in the autonomic nervous system and at vertebrate neuromuscular junctions (Dale, 1935), acetylcholine plays a central role in the control of wakefulness and REM sleep. Some have even gone as far as to call acetylcholine a neurotransmitter correlate of consciousness (Perry et al., 1999). 

ACh is necessary for control of skeletal muscle in verterbrates, acting as the neurotransmitter at the neuromuscular junction. It is also involved in transmission in the autonomic nervous system (see below, under "Neuroanatomy"). Central ACh is produced in two general areas in the brain incuding the basal forebrain (medial septal nuclei, diagonal band... 

The autonomic nervous system is itself divided into two parts the sympathetic and parasympathetic nervous systems. The sympathetic nervous system serves several glands and involuntary muscles. The primary neurotransmitter of the sympathetic nervous system is norepinephrine, which acts through a and p adrenergic receptors. 

The concept of chemical transmission in the nervous system arose in the early years of the century when it was discovered that the functioning of the autonomic nervous system was largely dependent on the secretion of acetylcholine and noradrenaline from the parasympathetic and sympathetic nerves respectively. The physiologist Sherrington proposed that nerve cells communicated with one another, and with any other type of adjacent cell, by liberating the neurotransmitter into the space, or synapse, in the immediate vicinity of the nerve ending. He believed that transmission across the synaptic cleft was unidirectional and, unlike conduction down the nerve fibre, was delayed by some milliseconds because of the time it took the transmitter to diffuse across the synapse and activate a specific neurotransmitter receptor on the cell membrane. 

Acetylcholine is the primary neurotransmitter in the parasympathetic division of the autonomic nervous system, which mainly innervates the gastrointestinal tract, eyes, heart, respiratory tract, and secretory glands. Although its receptors are crucial for maintaining all normal functions of the body, an extremely small number of illnesses can be explained by the dysfunction of cholinergic regions of the peripheral autonomic system. 

Morphologically, many synapses in the CNS appear to be quite similar to those for the peripheral autonomic nervous system. Electron microscopic studies have verified the similarities and have shown the presence of several types of storage vesicles in the areas of synapses. Neurons may synthesize, store, and release one or more transmitters. Many more synapses exist in the CNS than in the periphery, and many more neurotransmitters appear to be involved. 

D. Acetylcholine and norepinephrine are important neurotransmitters in the peripheral autonomic nervous system but are not nearly as prominent in the CNS. Glycine is a major inhibitory neurotrans-... 

Erection involves a coordinated action of the autonomic nervous system, and certain drugs may interfere with either the sympathetic division (e.g., aj- receptors) or the parasympathetic division (e.g., noncholinergic neurotransmitters). 

Dopamine, norepinephrine, and epinephrine (adrenalin) are biologically active amines that are collectively termed catecholamines. Dopamine and norepinephrine function as neurotransmitters in the brain and the autonomic nervous system. Norepinephrine and epinephrine are also synthesized in the adrenal medulla. 

FIGURE 18-2 Receptor classifications and subclassifications for acetylcholine (ACh] and norepinephrine [NE], the two primary neurotransmitters used in the autonomic nervous system. 

Acetylcholine A neurotransmitter in the somatic and autonomic nervous systems principal synapses using acetylcholine include the skeletal neuromuscular junction, autonomic ganglia, and certain pathways in the brain. 

Acetylcholine is a neurotransmitter that functions in conveying nerve impulses across synaptic clefts within the central and autonomic nervous systems and at junctures of nerves and muscles. Following transmission of an impulse across the synapse by the release of acetylcholine, acetylcholinesterase is released into the synaptic cleft. This enzyme hydrolyzes acetylcholine to choline and acetate and transmission of the nerve impulse is terminated. The inhibition of acetylcholineasterase results in prolonged, uncoordinated nerve or muscle stimulation. Organophosphorus and carbamate pesticides (Chapter 5) along with some nerve gases (i.e., sarin) elicit toxicity via this mechanism. 

Many theories have been proposed to explain migraine pathogenesis. Alterations in neurotransmitter systems (e.g., glutamate, nitric oxide, opioids), anatomical structures (e.g., the raphe system, vasculature), and the autonomic nervous system may be either primary or secondary factors in the evolution of a migraine attack. 

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